How would you offer being a surrogate mother?

Trigger warning ⚠️ infant loss

My Brother in-law and his wife have 5yr old daughter and recently had another baby that unfortunately didn’t survive long(1 month). The baby was born very early and ended up having a lot of complications. Their 5yr old was also born early but obviously survived. The mom has a lot of complications when she is pregnant and is also type 1 diabetic. They are pushing 40yrs old and I know they wanted this baby sooo much. The wife and I are kind of close(we talk weekly, mostly about our mother in-law lol) but my Brother in-law and her are also very private and live a little more on the “hippie” lifestyle than my husband and I do. Which is partly why I think they are more private, because we have different lifestyles.

How would you or should I not even offer, being a surrogate mother for them? Before this last baby was even born my sister in-law said they were done having kids. Since this lost this baby and she has a hard time with pregnancy I told my husband I’d like to offer to carry a baby for them. Thoughts? Opinions? How do you even say something that’s so serious and intimate to people?